Gearbox with passive lubrication system

ABSTRACT

A lubrication system includes a reserve housing configured to retain a lubrication fluid. A supply line in fluid communication with the reserve housing is configured to provide pressurized lubrication fluid to the reserve housing. An overflow tube has an overflow port, the overflow tube being configured to prevent the volume of the lubrication fluid from exceeding a certain amount. A metering jet is configured to allow the lubrication fluid to flow from the reserve housing onto a component, such as a bearing, in the gearbox at a predetermined rate. The metering jet provides flow of the lubrication fluid onto the bearing even when the supply line no longer provides pressurized lubrication fluid to the reserve housing.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/469,838, filed 31 Mar. 2011, titled “Gearbox with Passive LubricationSystem,” which is hereby incorporated by reference for all purposes asif fully set forth herein.

BACKGROUND

1. Technical Field

The present application relates to a passive lubrication system that isconfigured to provide lubrication in a gearbox during a loss oflubrication event.

2. Description of Related Art

Typically, a rotorcraft gearbox is required to have the capability tooperate for a specific period of time during which the primarylubrication pressure system has malfunctioned. One typical solution isfor the gearbox lubrication system to include a primary lubricationsystem and a completely redundant lubrication system. The redundantlubrication system is activated upon failure of the primary lubricationsystem. Having a completely redundant lubrication system addsconsiderable weight, complexity, and cost to the rotorcraft.

Hence, there is a need for an improved gearbox lubrication system.

DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the system of the presentapplication are set forth in the appended claims. However, the systemitself, as well as a preferred mode of use, and further objectives andadvantages thereof, will best be understood by reference to thefollowing detailed description when read in conjunction with theaccompanying drawings, wherein:

FIG. 1 is a schematic side view of a rotorcraft, according to anillustrative embodiment of the present application;

FIG. 2 is a partial schematic side view of the rotorcraft of FIG. 1,according to an illustrative embodiment of the present application;

FIG. 3 is a partial cross-sectional view of a gearbox, taken at sectionlines in FIG. 2, according to the preferred embodiment of the presentapplication;

FIG. 4A is a partial cross-sectional view of a gearbox, according to analternative embodiment of the present application; and

FIG. 4B is an enlarged view of a portion of the partial cross-sectionalview of the gearbox from FIG. 4A.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Illustrative embodiments of the system of the present application aredescribed below. In the interest of clarity, not all features of anactual implementation are described in this specification. It will ofcourse be appreciated that in the development of any such actualembodiment, numerous implementation-specific decisions must be made toachieve the developer's specific goals, such as compliance withsystem-related and business-related constraints, which will vary fromone implementation to another. Moreover, it will be appreciated thatsuch a development effort might be complex and time-consuming but wouldnevertheless be a routine undertaking for those of ordinary skill in theart having the benefit of this disclosure.

In the specification, reference may be made to the spatial relationshipsbetween various components and to the spatial orientation of variousaspects of components as the devices are depicted in the attacheddrawings. However, as will be recognized by those skilled in the artafter a complete reading of the present application, the devices,members, apparatuses, etc. described herein may be positioned in anydesired orientation. Thus, the use of terms such as “above,” “below,”“upper,” “lower,” or other like terms to describe a spatial relationshipbetween various components or to describe the spatial orientation ofaspects of such components should be understood to describe a relativerelationship between the components or a spatial orientation of aspectsof such components, respectively, as the device described herein may beoriented in any desired direction.

The system of the present application includes a passive lubricationsystem that is configured to provide continual lubrication to gearboxcomponents for a period of time during a “run dry” or emergencycondition. A “run dry” condition can exist when the primary pressurizedlubrication supply has been terminated through a system malfunction,battle damage, or the like. During the run dry scenario, the passivelubrication system of the present application provides continuedlubrication to gearbox components without active command.

Referring to FIGS. 1 and 2 in the drawings, a rotorcraft 101 isillustrated. Rotorcraft 101 has a rotor system 103 with a plurality ofmain rotor blades 111. Rotorcraft 101 further includes a fuselage 105,landing gear 107, a tail member 109, and tail rotor blades 113. Anengine 115 supplies torque to a main rotor mast 117 via a gearbox 327for the rotating of main rotor blades 111. Engine 115 also suppliestorque to a tail rotor drive shaft 119 for the rotating of tail rotorblades 113. The pitch of each main rotor blade 111 can be selectivelycontrolled in order to selectively control direction, thrust, and liftof rotorcraft 101. Further, the pitch of tail rotor blades 113 can beselectively controlled in order to selectively control yaw of rotorcraft101. Rotorcraft 101 is illustrated for exemplary purposes only. Itshould be appreciated that the system of the present application may beused on aircraft other than rotorcraft, such as airplanes, tilt rotors,unmanned aircraft, to name a few examples. Further, the system of thepresent application may be used on non-aircraft vehicles andimplementations.

Referring now also to FIG. 3, a passive lubrication system 301 isillustrated in conjunction with gearbox 327. In the illustratedembodiment, gearbox 327 is depicted as a gearbox on rotorcraft 101;however, it should be appreciated the system 301 may be equallyimplemented on a variety of vehicles and structures having gearboxesthat require lubrication. Gearbox 327 functions to convert high speedrotation of an output drive shaft of engine 115 into low speed rotationof main rotor mast 117. Gearbox 327 includes a plurality of gears andbearings that require lubrication to properly function.

Lubrication of gearbox 327 is essential to the operation of rotorcraft101. Rotorcraft regulatory agencies, such as the Federal AviationAdministration (FAA) may require that gearbox 327 be operable for arequisite period of time after the primary pressurized lubricationsystem has failed. Such a requirement in a rotorcraft gearbox may bereferred to as “run dry” capability requirement.

System 301 includes a reserve housing 303 configured to contain acertain volume of lubrication fluid 321. Reserve housing 303 ispreferably cast or machined such that reserve housing 303 is astructural member capably of carrying loads. In such an embodiment,reserve housing 303 is integral with the gearbox housing such that thegearbox housing and the reserve housing 303 are a single cast ormachined structure. Reserve housing 303 can alternatively be a separateunit from the gearbox housing, such that reserve housing 303 can beattached to the gearbox housing with one or more fasteners and seals,for example. A lubrication fluid supply line 323 provides pressuredlubrication fluid to the interior of reserve housing 303 during normaloperating conditions. Furthermore, the pressurized primary lubricationsystem that provides pressurized lubrication fluid to lubrication fluidsupply line 323 can be configured to provide lubrication to the interiorof the gearbox in other locations as well.

System 301 preferably further includes an overflow tube 305 having anoverflow entry port 307. Overflow tube 305 is at least partly configuredto prevent the volume of lubrication fluid 321 within reserve housing303 to exceed a predefined level dictated by the location of overflowentry port 307. During normal operation, lubrication fluid supply line323 continuously provides pressurized lubrication fluid 321 to theinterior of housing 303. As such, lubrication fluid 321 enters overflowentry port 307 and is gravity fed down through the interior of overflowtube 305 and through an overflow exit port 309, along an overflowdirection 311 into gearbox 327. Overflow tube 305 can include a filteror screen for removing any undesired contamination from lubricationfluid 321. Overflow tube 305 is preferably removable, via a fastener, inorder to facilitate inspection and maintenance. One or more seals can beused to prevent leakage of lubrication fluid 321 between overflow tube305 and reserve housing 303. Overflow tube 305 is also configured to actas a vent to allow air to flow to/from the interior of reserve housing303 to/from the interior of gearbox 327. For example, air can flowthrough overflow tube 305 when supply line 323 fills reserve housing303. Similarly, air can flow into reserve housing 321 when lubricationfluid 321 drains out through metering jet 313 so as to prevent a vacuumfrom forming therein.

It should be appreciated that supply line 323 can include a check valvein order to prevent lubrication fluid 321 from flowing back down supplyline 323. In an alternative embodiment, supply line 323 is located on aside portion of reserve housing 103, which can cause a check valve insupply line 323, or other means of preventing reverse flow oflubrication fluid 321, to be particularly desirable.

System 301 preferably also includes a metering jet 313. In theillustrated embodiment, metering jet 313 includes a plurality ofmetering jet orifices 315. Orifices 315 are configured to receivelubrication fluid 321, which is gravity fed through a metering jet exitport 317. Flow of lubrication fluid 321 is metered through metering jet313 between orifices 315 and exit port 317 along a direction 319, andonto a bearing 325. Metering jet 313 preferably includes a filter orscreen for removing any undesired contamination from lubrication fluid321. Metering jet 313 is preferably removable, via a fastener, in orderto facilitate inspection and maintenance. One or more seals can be usedto prevent leakage of lubrication fluid 321 between metering jet 313 andreserve housing 303.

During a loss of lubrication situation, the lubrication supply fromsupply line 323 can cease to supply lubrication fluid 321 to housing303. Even though lubrication fluid 321 is not being pressure fed intohousing 303, system 301 is configured to continuously supply lubricationfluid 321 to bearing 325 until reserve housing 303 is emptied oflubrication fluid 321. Reserve housing 303, orifices 315, and exit port317 are all configured so the lubrication fluid 321 is metered andallowed to flow onto bearing 325 for a requisite period of time. Forexample, the requisite period of time may be thirty minutes. Therequisite period of time allows the pilot of the rotorcraft to safelyland while the gearbox 327 is operable.

System 301 is configured to be passive in that it operates to providelubrication fluid 321 to bearing 325 during a loss of lubricationsituation without requiring an affirmative command from separate entity,such as pilot or detection system. Further, system 301 is configured topassively provide lubrication fluid 321 to one or more bearings 325 fora period of time so as to satisfy a “run dry” requirement.

System 301 is also configured such that the lubrication fluid 321 inreserve housing 303 is continuously heated, circulated, and filteredduring normal operating conditions. More specifically, normal operatingconditions allow for the continuous introduction of lubrication fluid321 into reserve housing 303 via supply line 323, as well as thecontinuous flow of lubrication fluid 321 from reserve housing 303 intogearbox 327 through overflow exit port 309 and metering jet exit port317. The continual exchange of lubrication fluid 321 in reserve housing303 insures that lubrication fluid 321 is in condition for use uponfailure of the primary pressurized lubrication system.

Even though system 301 is illustrated as having only one overflow tube305 and one metering jet 313, it should be appreciated that system 301may include a plurality of overflow tubes 305 and metering jets 313. Forexample, each metering jet 313 may be strategically located abovecritical bearings which need lubrication fluid 321 for operation ofgearbox 327. It should be appreciated that the bearings receivinglubrication fluid 321 via metering jet 313 may also be gears, or anyother type of moving part that may require lubrication to minimizefriction.

Referring now also to FIGS. 4A and 4B in the drawings. As shown in FIG.4A the reserve housing 303 is a separate unit from the gearbox housing.As shown in FIG. 4B the metering jet 313 preferably includes a filter orscreen for removing any undesired contamination from lubrication fluid321.

The passive lubrication system 301 provides significant advantages,including: 1) passively lubricating the gearbox during a failure of aprimary pressurized lubrication system; and 2) providing heated,filtered, and circulated lubrication fluid that is available during thefailure of a primary pressurized lubrication system.

It is apparent that a system with significant advantages has beendescribed and illustrated. Although the system of the presentapplication is shown in a limited number of forms, it is not limited tojust these forms, but is amenable to various changes and modificationswithout departing from the spirit thereof.

The invention claimed is:
 1. A lubrication system for a gearbox, thelubrication system comprising: a reserve housing configured to retain alubrication fluid; a supply line in fluid communication with the reservehousing, the supply line configured to provide pressurized lubricationfluid to the reserve housing; an overflow tube directly coupled betweenthe reserve housing and the gearbox, the overflow tube having anoverflow entry port and an overflow exit port, the overflow tube beingconfigured to prevent a volume of the lubrication fluid in the reservehousing from exceeding a predefined level; and a metering jet coupled tothe reserve housing adjacent the overflow tube being configured to allowthe lubrication fluid to flow from the reserve housing onto a componentin the gearbox at a predetermined rate, the metering jet metering theflow of lubrication fluid through at least one orifice, the metering jetfiltering contaminants from the lubrication fluid and providing passivefiltration and flow of lubrication fluid; wherein the metering jetprovides flow of the lubrication fluid onto the component for a periodof time subsequent to a cessation of flow of the lubrication from thesupply line to the reserve housing; wherein the metering jet includes anexit port on a lowest surface of the metering jet relative to thepredefined level in the reserve housing, the exit port being configuredto allow the lubrication fluid to exit the metering jet; wherein theoverflow exit port is located below the overflow entry port; wherein theoverflow exit port is configured to allow the lubrication fluid to flowfrom the reserve housing directly into the gearbox; and wherein theoverflow tube is configured to act as a vent to allow air to exchangebetween an interior of a gearbox housing and the interior of the reservehousing.
 2. The lubrication system according to claim 1, wherein thereserve housing is integral with the gearbox housing.
 3. The lubricationsystem according to claim 1, wherein the reserve housing is a separatemember attached to the gearbox housing.
 4. The lubrication systemaccording to claim 1, wherein the metering jet includes a plurality oforifices configured to allow the lubrication fluid to enter an interiorof the metering jet.
 5. The lubrication system according to claim 1,wherein the metering jet is removable from the reserve housing.
 6. Thelubrication system according to claim 1, wherein the overflow tube isremovable from the reserve housing.
 7. The lubrication system accordingto claim 1, wherein the component is at least one of: a bearing; and agear.
 8. The lubrication system according to claim 1, wherein the supplyline is associated with an upper portion of the reserve housing.
 9. Agearbox for an aircraft, the gearbox comprising: a gearbox housing forhousing a plurality of components; a reserve housing configured toretain a lubrication fluid, the lubrication fluid being filtered withinthe gearbox; a supply line in fluid communication with the reservehousing, the supply line configured to provide pressurized lubricationfluid to the reserve housing; an overflow tube directly coupled betweenthe gearbox housing and the reserve housing, the overflow tube having anoverflow port, the overflow tube being configured to prevent a volume ofthe lubrication fluid in the reserve housing from exceeding a predefinedlevel; the overflow tube further comprising; an overflow exit port influid communication with the overflow port so that the lubrication fluidcan flow from the overflow port, through an interior of the overflowtube, and out the overflow exit port into the gearbox housing; and ametering jet coupled to the reserve housing adjacent the overflow tubebeing configured to allow the lubrication fluid to flow from the reservehousing onto at least one of the plurality of components in the gearboxat a predetermined rate; wherein the metering jet includes an exit porton a lowest surface of the metering jet relative to the predefined levelin the reserve housing, the exit port being configured to allow thelubrication fluid to exit the metering jet; wherein the metering jetprovides passive flow of the lubrication fluid onto a bearing for aperiod of time subsequent to a cessation of flow of the lubrication fromthe supply line to the reserve housing; wherein the overflow exit portis lower than the overflow port; and wherein the bearing is located inthe gearbox housing.
 10. The gearbox according to claim 9, wherein theoverflow port is a cutout in the overflow tube.
 11. The gearboxaccording to claim 9, wherein the period of time is at least thirtyminutes.
 12. The gearbox according to claim 9, wherein the plurality ofcomponents in the gearbox are moveable objects that require lubricationto minimize friction.
 13. The gearbox according to claim 9, wherein thelubrication fluid is filtered within the metering jet.
 14. The gearboxaccording to claim 9, wherein the lubrication fluid is filtered withinthe overflow tube.
 15. The gearbox according to claim 9, wherein theoverflow tube is configured to act as a vent to allow air to exchangebetween the interior of the gearbox housing and the interior of thereserve housing.